In recent years, environmental standards have markedly affected the requirements for wastewater treatment. Effluent standards have become more stringent, and it also has become important to develop wastewater treatment processes that are capable of providing wastewater suitable for reuse.
The problems of wastewater treatment have been particularly important, for example, in the dairy industry and in the treatment of leachates from hazardous wastewater impoundments and waste disposal sites. The nation's dairy plants process billions of pounds of milk annually, and the processing of such large volumes of material inevitably produces a large volume of waste that includes an extremely high level of organic compositions. Leachates from hazardous waste contain many priority pollutants, both inorganic and organic. The Environmental Protection Agency has estimated that from 41 to 57 million metric tons of industrial hazardous waste are produced each year and that some 32,000 to 50,000 wastewater impoundments and waste disposal sites in the United States produce leachate, which can cause major groundwater contamination.
Existing processes for the treatment of organic wastes have significant drawbacks, particularly with respect to the removal of organic substances which are non-biodegradable or which biodegrade slowly. In the United States, the predominant method of biological treatment is through use of activated sludge, but biological treatment processes are relatively inefficient, produce a large volume of sludge that must be disposed of, and frequently do not meet current waste quality discharge requirements for the removal of non-biodegradable or slowly biodegradable organic substances. Physiochemical processes, such as activated carbon adsorption, have been designed to remove non-biodegradable or slowly biodegradable organic compounds, but are energy and operating cost intensive.
A paper, entitled "Powdered Activated Carbon Treatment (PACT.sup..TM.) of Leachate from the Stringfellow Quarry" and presented at an EPA Research Symposium at Cincinnati, Ohio on about Apr. 30, 1985, discusses treatment of a high priority wastewater leachate containing halogenated and non-halogenated volatile organics as well as heavy metals, by first pretreating the waste by lime precipitation to remove heavy metals and then treating the settled wastewater in the aeration tank, to which activated carbon had been added, of a generally conventional activated sludge system. This system is said to present several advantages over conventional activated sludge processes, but considerable further improvement is still desirable.